Cryogenic media such as liquid nitrogen or liquid air are utilized in cryopreservation for preserving biological samples at a very cold temperature (e.g. 196 degree Celsius below zero). According to some vitrification protocols, the biological sample, e.g. an oocyte or an embryo, is plunged the cryogenic medium, thus resulting in very high cooling rates, which facilitates vitrification rather than crystallization of the intracellular and intercellular liquids. Cryogenic media such as liquid nitrogen or liquid air may also have culinary applications, for example in preparing ice-creams and cold cocktails. However, commercially available cryogenic media, such as liquid nitrogen, are in many cases not sufficiently clean for those applications.
In cryopreservation, biological samples stored in liquid nitrogen might be contaminated with viruses, germs, fungi and spores. In some cases, contamination might be due to contaminations already residing in the liquid nitrogen when supplied to the laboratory. Additionally or alternatively, contamination might also be due to cross-contamination between samples.
The potential of disease transmission and pathogen survival through contaminated cryogenic medium has been proposed by many authors and the evidence of contamination in human patients has been described for different pathogens. For example, the publication “Microbial contamination of embryos and semen during long term banking in liquid nitrogen” (Bielanski A, Bergeron H, Lau P C, Devenish J. Cryobiology 2003; 46:146-52), reports on microbial contamination of embryos and semen cryopreserved in sealed plastic straws and stored for 6-35 years in liquid nitrogen.
Therefore, the use of safe cryopreservation protocols is important to prevent potential contamination of the biological samples by the cryogenic medium.